WO2018147714A1 - Separation film for lithium secondary battery having adhesive layer - Google Patents

Abstract

The present invention relates to a coating composition, comprising a solvent, inorganic particles, a dispersant, and a binder, for coating at least one surface of a porous substrate having a plurality of pores. The binder comprises binder B and binder A, wherein the binder B and the binder A both contain a vinylidene fluoride (VDF)-derived unit and a hexafluoropropylene (HFP)-derived unit. The HFP-derived unit accounts for 8% to 50% by weight of the binder B, and in the binder A, the HFP-derived unit is not more than 80% of the proportion thereof in the binder B and is not less than 5% by weight of the binder A. The total number average molecular weight of the binder B is 200,000 to 2,000,000, and the total number average molecular weight of the binder A is 70% or less of that of the binder B. The weight ratio of binder A: binder B in the total coating composition is 0.1 to 10: 1. The present invention has resolved the problem that when a binder is thinned from 4㎛ to 3㎛, the binder is dried before being sufficiently phase-separated and thus a sufficient electrode adhesive force cannot be obtained, and also in terms of a manufacturing method, the present invention has provided a coating composition in which sufficient phase separation occurs even in a low-humidity condition.

Description

Separator for Lithium Secondary Battery with Adhesive Layer

The present invention relates to a coating composition for a lithium secondary battery separator having an adhesive layer, and more particularly, to a coating composition for a lithium secondary battery separator having an adhesive layer for coating at least one surface of a porous substrate separator having a plurality of pores.

Recently, as the light weight and high functionality of portable devices such as smartphones, laptops, tablet PCs, and portable game machines are advanced, demand for secondary batteries used as driving power sources is increasing. In the past, nickel-cadmium, nickel-hydrogen, nickel-zinc batteries and the like have been used. Currently, lithium secondary batteries with high operating voltage and high energy density per unit weight are used.

The lithium secondary battery may cause an explosion due to heat generation depending on the usage environment. In order to solve the safety problem of the lithium secondary battery, there is a great interest in a separator, particularly a technology for increasing the bonding force between the porous coating layer and the electrode of the separator. Strong bonding of the separator and the electrode can increase the safety of the battery. There is a need for technology development for a binder that suppresses an increase in the interfacial resistance between the separator and the electrode due to an electrode side reaction generated during a cycle and improves air permeability, and a separator using the same.

Patent Literature 1 includes a separator including an adhesive layer and a separator applicable to a secondary battery as a secondary battery using the same, and a secondary battery capable of maintaining the shape stability and adhesion of the battery even after charging and discharging, which is an environment in which an actual battery is used. to provide.

Patent document 1 is a porous base material; And an adhesive layer formed on one or both sides of the substrate, wherein the adhesive layer includes a vinylidene fluoride-derived unit and a polyvinylidene fluoride (PVDF) system having a hexafluoropropylene (HFP) -derived unit content of 5% by weight or less. A polyvinylidene fluoride (PVDF) comprising a first binder, a vinylidene fluoride derived unit and a hexafluoropropylene (HFP) derived unit, wherein the hexafluoropropylene (HFP) derived unit content is 10 to 30% by weight; A second binder, wherein the weight ratio of the polyvinylidene fluoride (PVDF) -based first binder and the polyvinylidene fluoride (PVDF) -based second binder is 0.5: 9.5 to 2: 8, and includes the separator. It relates to a secondary battery.

Patent document 2 relates to a separator having a binder layer, an electrochemical device including the separator, and a manufacturing method of the separator, in order to solve the safety problem of the secondary battery, the bonding strength of the separator, in particular, the porous coating layer of the separator and the electrode. It was raised. The strong bonding of the separator and the electrode enhances the safety of the battery, and provides a binder that suppresses an increase in the interfacial resistance between the separator and the electrode due to an electrode side reaction generated during the cycle and improves air permeability.

Patent Literature 2 includes a porous substrate, a porous coating layer and a binder layer, wherein the binder present in the porous coating layer and the binder layer includes two or more polyvinylidene flues having a hexafluoropropylene (HFP) content difference of 3% by weight or more. Separation membranes are provided that include a vinylidene (PVDF) homopolymer or a polyvinylidene fluoride-co-hexafluoropropylene (P (VDF-HFP)) based copolymer. Forming a binder solution, forming a slurry, and forming a porous coating layer, wherein the binder in the binder solution comprises at least two PVDF homopolymers or P (VDF-HFP) -based air having a HFP content difference of at least 3% by weight; Also provided is a method of preparing a separator comprising coalescing.

Patent document 3 relates to a battery cell including a separator with enhanced adhesion, even if the organic-inorganic porous coating layer is coated on a porous polymer substrate with a thin thickness to exhibit excellent adhesion to the electrode, it is possible to improve the thermal shrinkage of the separator Provide a separator.

Patent document 3 is a battery cell in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is built in a battery case, wherein the separator is on at least one surface of the porous polymer substrate and the porous polymer substrate Including an organic-inorganic porous coating layer formed, the organic-inorganic porous coating layer, inorganic particles including a mixture of metal oxide and metal hydroxide, PVDF-HFP polymer binder having a high hexafluoropropylene (HFP) content (' PHFP high ') and a mixture of PVDF-HFP polymer binder (' PHFP low ') having a low HFP content, the separator, and the adhesion between the positive electrode or the negative electrode relates to a battery cell characterized in that more than 15gf / 25mm .

Patent document 4 relates to an electrode having an improved adhesive force and a lithium secondary battery including the same, and provides a method capable of increasing the binding force between the electrode current collector and the electrode mixture layer and reducing the binder content contained in the electrode mixture layer.

Patent document 4 is an electrode in which an electrode mixture containing an electrode active material is coated on an electrode current collector, wherein the electrode mixture includes a mixture of two or more binders having different specific gravity.

However, the demand for thinning of secondary battery separators is steadily increasing, and in recent years, attempts have been made to thinner the binder layer (cross section basis) of the separator to 3 μm or less. Typically, the binder layer of the separator of a lithium secondary battery uses a method of inducing phase separation so that a binder is widely distributed on the surface by coating a slurry including a solvent, a binder, a dispersant, and inorganic particles under humidification. Such a method is very sensitive to humidification conditions, and various changes in phase separation form may occur depending on humidity conditions, and in some cases, an adhesive layer may not sufficiently apply a surface.

In addition, when the phase is sufficiently dried before the adhesive layer is not formed on the surface does not implement sufficient adhesive strength. In the case of inducing phase separation or applying a binder having a very high phase separation rate, the adhesion between the porous substrate and the coating layer and the binding force between the inorganic particles may be lowered.

Particularly, when the thickness of the coating layer is thinned from 4 μm or more to 3 μm, a problem arises in that the binder is dried before sufficient phase separation to obtain sufficient electrode adhesion. When coating more than 4㎛ based on the cross section (Fig. 1 (a)) by using the prior art, the adhesive layer is separated and positioned on the surface side, but when the thin film is coated on the thickness of 3㎛ or less (Fig. 1 (b)), the adhesive layer is not separated and sufficient adhesive strength with the electrode Is not implemented (see FIG. 1). In the prior art, two or more binders having different composition ratios of PVDF and HPF were used similarly to the present invention, but both could not provide the desired electrode adhesion through sufficient phase separation for the thin film coating at both humidification conditions and 3 μm.

(Patent Document 0001) Republic of Korea Patent Publication No. 10-2016-0117962

(Patent Document 0002) Republic of Korea Patent Publication No. 10-2014-0050877

(Patent Document 0003) Republic of Korea Patent Publication No. 10-2016-0108116

(Patent Document 0004) Republic of Korea Patent Publication No. 10-2013-0117350

As described above, an object of the present invention is to provide a coating composition for a separator in which the bonding force between the porous coating layer and the electrode of the separator is increased. Specifically, the present invention increases the safety of the battery through strong bonding of the separator and the electrode, suppresses the increase in the interfacial resistance of the separator and the electrode by the electrode side reaction generated during the cycle, the coating composition for a separator comprising a binder to improve the air permeability To provide. Particularly, when the coating layer (cross section basis) of the separator was thinned from 4 μm to 3 μm, the binder was dried before sufficient phase separation, and sufficient electrode adhesion was not obtained. Also, in the manufacturing method, sufficient phase separation was achieved even under low humidity conditions. It is intended to provide a coating composition that can occur.

The present invention for solving the above problems is a coating composition comprising a solvent, an inorganic particle, a dispersant, a binder for coating at least one surface of a porous substrate having a plurality of pores, the binder is binder B and binder A Wherein both the binder B and the binder A include a vinylidene fluoride (VDF) derived unit and a hexafluoropropylene (HFP) derived unit, wherein the HFP derived unit accounts for 8 to 50% by weight of the binder B, and the binder In A, it is 80% or less of the ratio of binder B and 5% by weight or more of binder A, the total number average molecular weight of binder B is 200,000 to 2 million, and the total number average molecular weight of binder A is 70% or less of binder B. , To provide a coating composition wherein the weight ratio of binder A: binder B in the total coating composition is 0.1 to 10: 1.

The binder B and the binder A may be composed of vinylidene fluoride (VDF) and hexafluoropropylene (HFP).

Vinylidene fluoride-derived copolymers including poly (vinylidene fluoride-co-chlorotrifluoroethylene, poly (vinylidene fluoride-co-trifluoroethylene), etc., in addition to binder B and binder A, polymethylmetha Polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-co-vinyl acetate, polyethylene oxide Cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyano Cyanoethylcellulose, cyanoethylsucrose, Pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, or polyimide, alone or in combination of two or more thereof May be included as an additional binder.

The porous substrate is polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polyamide, poly Carbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polybenzimidazole, polybenzimidazole Any one polymer selected from the group consisting of polyethersulfone, polyphenyleneoxide, cyclic olefin high polymer, cyclicolefin copolymer, polyphenylenesulfide and polyethylenenaphthalene Tombs formed from mixtures of more than one species A film or a multi-film, a woven fabric or nonwoven fabric.

The dispersant is one or a mixture of two or more selected from the group consisting of acrylic copolymers, and the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transfer ability, and mixtures thereof. .

The inorganic particles may be formed of two or more kinds of different sizes. For example, the inorganic particles A having a D50 of 200 nm to 1 μm and the D50 may be composed of an inorganic B having 70% or less of the inorganic particles A.

The content of the binder is 3 to 50 parts by weight based on 100 parts by weight of the inorganic particles, and the content of the dispersant is 0.5 to 5 parts by weight based on 100 parts by weight of the inorganic particles.

The present invention provides a separator coated by the coating composition. At this time, the thickness of the coating is 3㎛ or less based on the cross section.

The present invention provides an electrochemical device, preferably a lithium secondary battery comprising a positive electrode, a negative electrode, and the separator interposed between the positive electrode and the negative electrode.

In the method for preparing a separator by coating at least one side of the porous substrate having a plurality of pores using the coating composition of the present invention, the humidification conditions are provided in 35 to 45% coating thickness of 3㎛ or less do.

1 is a photograph observing the phenomenon occurring during the coating 4a or more coating (a) and 3㎛ or less thin film coating (b) using a conventional technique with an electron microscope.

2 is a photograph of an embodiment according to the present invention observed with an electron microscope.

Figure 3 is a photograph of the Comparative Example 1 according to the present invention observed with an electron microscope.

Figure 4 is a photograph of the Comparative Example 2 according to the present invention observed with an electron microscope.

Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in this specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors should properly introduce the concept of terms in order to best explain their own inventions. It should be interpreted as meanings and concepts in accordance with the technical spirit of the present invention based on the principle that it can be defined. Therefore, the configurations presented in the embodiments described herein are only one of the most preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, and various equivalents may be substituted for them at the time of the present application. It should be understood that there may be variations.

The present invention provides a coating composition comprising a solvent, inorganic particles, a dispersant, and a binder for coating at least one side of a porous substrate having a plurality of pores.

1) porous substrate

The porous substrate is polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate (polycarbonate), polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyether Any one polymer selected from the group consisting of sulfon (polyethersulfone), polyphenylene oxide, cyclic olefin high polymer (cyclic olefin copolymer), polyphenylene sulfide and polyethylene naphthalene (polyethylenenaphthalene) or two of them Polymer membrane formed of the above mixture It may be those of a multi-film, a woven or non-woven fabric, but are not limited to.

The thickness of the porous substrate is not particularly limited, but may be about 5 to about 50 μm, and the pore size and pore present in the porous substrate are also not particularly limited, but about 0.01 to about 50 μm, and about 10 to about 95, respectively. May be%.

2) solvent

As a solvent, the solubility index is similar to the binder to be used, and the boiling point is preferably low. This is because mixing can be made uniform, and then the solvent can be easily removed. In particular, the solvent is preferably a polar solvent having a boiling point of less than 100. However, in the case of a nonpolar solvent, it is not preferable because there exists a possibility of the fall of dispersion force.

Non-limiting examples of solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (Nmethyl- 2-pyrrolidone, NMP), cyclohexane (cyclohexane), water, etc. may be one or a mixture of two or more selected from the group consisting of.

The solvent comprises about 50 parts by weight to about 90 parts by weight based on 100 parts by weight of the total amount of solids and the solvent, that is, 100 parts by weight of the total amount of the solid mixture of the inorganic material, the binder, and the dispersant and the solvent (eg, the polar solvent). If the solvent is less than 50 parts by weight based on 100 parts by weight of the total content of the solid and the solvent, the coating property is deteriorated due to the increase in viscosity, a great difficulty in forming the binder layer exists, and there is a difficulty in thinning the film. It can lead to a decrease and an increase in manufacturing cost.

3) inorganic particles

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as the oxidation and / or reduction reactions do not occur in the operating voltage range (for example, 0 to about 5 V on the basis of Li / Li +) of the electrochemical device to be applied. In particular, in the case of using the inorganic particles having the ion transport ability, it is possible to improve the performance by increasing the ion conductivity in the electrochemical device.

In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the dissociation degree of the electrolyte salt such as lithium salt in the liquid electrolyte.

For the foregoing reasons, the inorganic particles may include high dielectric constant inorganic particles having a dielectric constant of about 5 or more, such as about 10 or more, inorganic particles having a lithium ion transfer ability, or a mixture thereof. Non-limiting examples of inorganic particles having a dielectric constant of about 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), Hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, Al (OH) _3, or mixtures thereof.

The inorganic particles having a lithium ion transfer capacity refers to inorganic particles containing lithium elements but having a function of transferring lithium ions without storing lithium, and the inorganic particles having lithium ion transfer ability are present in the particle structure. Since the lithium ions can be transferred and moved due to a kind of defect, the lithium ion conductivity in the battery is improved, thereby improving battery performance. Non-limiting examples of the inorganic particles having a lithium ion transfer capacity include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (LixTiy (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), lithium aluminum (LiAlTiP) such as LixAlyTiz (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O _5, etc. _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li _3.25 Ge _0.25 P _0.75 Lithium germanium thiophosphate such as S ₄ (LixGeyPzSw, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), lithium nitride such as Li ₃ N (LixNy, 0 SiS ₂ series glass (Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0) such as <x <4, 0 <y <2), Li ₃ PO ₄ -Li ₂ S-SiS _2, etc. <z <4), P ₂ S ₅ series glass (Li _x P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7), such as LiI-Li ₂ SP ₂ S ₅ , or these And mixtures thereof.

The inorganic particle size is not limited, but may be about 0.01 to about 10 μm, or about 0.05 to about 1.0 μm, as much as possible for uniform coating thickness formation and proper porosity. When the size of the inorganic particles satisfies the above range, the dispersibility is improved to easily control the physical properties of the separator, the thickness of the porous coating layer is increased to decrease the mechanical properties or due to excessively large pore size during battery charging and discharging The problem of an internal short circuit can be prevented. In addition, the inorganic particles may be composed of two or more kinds of different sizes. For example, the inorganic particles A having a D50 of 200 nm to 1 μm and the D50 may be composed of an inorganic B having 70% or less of the inorganic particles A.

4) Dispersant

The dispersant may be one or a mixture of two or more selected from the group consisting of acrylic copolymers. This dispersant functions as an excellent dispersant for improving the dispersibility of inorganic matter. In addition, the dispersant has an excellent function as the dispersant and a function as a binder having adhesion.

This dispersant comprises a polar group, by having such a polar group can interact with the surface of the inorganic material to increase the dispersibility of the inorganic material. In addition, the dispersant is easy to control the physical properties of the dispersing and the adhesion can be improved in the balance it can contribute to the stability of the separator and the electrochemical device using the separator.

The acrylic copolymer may be a copolymer including one or two or more functional groups selected from the group consisting of OH, COOH, CN, amine and amide groups.

This acrylic copolymer may be a copolymer comprising at least one first functional group and at least one second functional group. Here, the first functional group may be selected from the group consisting of OH groups and COOH groups, and the second functional group may be selected from the group consisting of amine groups and amide groups. At this time, when using a polymer having an OH group or a COOH group alone, there is a problem that the adhesive force increases but the dispersion force is lowered and the coating does not occur uniformly. On the other hand, when a polymer having an amine group and / or an amide group is used alone, there is still a concern that the dispersing force is increased but the adhesion with the porous separator substrate may be low. Therefore, by using a copolymer comprising at least one functional group selected from the group consisting of OH groups and COOH groups as the first functional group and at least one functional group selected from the group consisting of amine groups and amide groups as the second functional group, Uniform coatings with harmonically improved dispersibility can be provided to provide prevention of coating layer detachment and electrochemical stability.

The acrylic copolymer may have a repeating unit derived from a monomer having a first functional group and a repeating unit derived from a monomer having a second functional group.

Non-limiting examples of the monomer having the first functional group include (meth) acrylic acid, 2- (meth) acryloyloxy acetic acid, 3- (meth) acryloyloxy propyl acid, 4- (meth) acryloyloxy Butyric acid, acrylic acid duplex, itaconic acid, maleic acid, maleic anhydride, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 2-hydroxyethylene glycol (meth) acrylate and 2-hydroxypropylene glycol (meth) acrylate selected from the group consisting of It may be one or more.

The monomer having the second functional group may include at least one of an amine group and an amide group in a side chain thereof, and non-limiting examples thereof include 2-(((butoxyamino) carbonyl) oxy) ethyl (meth) Acrylate, 2- (diethylamino) ethyl (meth) acrylate, 2- (dimethylamino) ethyl (meth) acrylate, 3- (diethylamino) propyl (meth) acrylate, 3- (dimethylamino) Propyl (meth) acrylate, methyl 2-acetoamido (meth) acrylate, 2- (meth) acrylamidoglycolic acid, 2- (meth) acrylamido-2-methyl-1-propanesulfonic acid, ( 3- (meth) acrylamidopropyl) trimethyl ammonium chloride, N- (meth) acryloyl amido-ethoxyethanol, 3- (meth) acryloyl amino-1-propanol, N- (butoxymethyl) (Meth) acrylamide, N-tert-butyl (meth) acrylamide, diacetone (meth) acrylamide, N, N-dimethyl (meth) acrylamide De, N- (isobutoxymethyl) acrylamide, N- (isopropyl) (meth) acrylamide, (meth) acrylamide, N-phenyl (meth) acrylamide, N- (tris (hydroxymethyl) methyl) (Meth) acrylamide, N-N '-(1,3-phenylene) dimaleimide, N-N'-(1,4-phenylene) dimaleimide, N-N '-(1,2- Dihydroxyethylene) bisacrylamide, N-N'-ethylenebis (meth) acrylamide, and N-vinylpyrrolidinone.

Examples of such acrylic copolymers include ethyl acrylate-acrylic acid-N, N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2- (dimethylamino) ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N, N And one or more selected from the group consisting of -diethylacrylamide copolymer and ethyl acrylate-acrylic acid-2- (diethylamino) ethyl acrylate copolymer.

The content of the dispersant may be 0.5 to 5 parts by weight based on 100 parts by weight of the inorganic particles.

5) Binder

The binder includes binder B and binder A, wherein binder B and binder A both include vinylidene fluoride (VDF) derived units and hexafluoropropylene (HFP) derived units, and the HFP derived units are represented by 8 To 50% by weight, preferably 8 to 40% by weight, more preferably 8 to 30% by weight, even more preferably 8 to 20% by weight, most preferably 10 to 15% by weight, and in binder A, It is 80% or less of the ratio of binder B and 5% by weight or more of binder A, and the total number average molecular weight of binder B is 200,000 to 2 million, preferably 300,000 to 1.5 million, and even more preferably 400,000 to 120. However, most preferably 500,000 to 1 million, the total number average molecular weight of binder A is 70% or less of binder B, and the weight ratio of binder A: binder B in the total coating composition is 0.1 to 10: 1, preferably 0.3 Not 8: 1, more preferably 0.5 to 6: 1, even more preferably 0.7 to 4: 1, most preferably from 0.8 to 2: 1 in a coating composition. If the content of binder A is lower than the above range, it is dried before phase separation to obtain sufficient electrode adhesion. If the content of binder A is high, the adhesion is sharp at 3 μm, which is high in electrical resistance or thin coating thickness. There is a problem falling.

Vinylidene fluoride-derived copolymer including poly (vinylidene fluoride-co-chlorotrifluoroethylene, poly (vinylidene fluoride-co-trifluoroethylene), etc., in addition to binder B and binder A, polymethylmetha Polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-co-vinyl acetate, polyethylene oxide, Cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethyl Cellulose (cyanoethylcellulose), cyanoethyl sucrose (cyanoethylsucrose), Pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide, or a mixture of two or more thereof It can be included as an additional binder.

The content of the binder may be 3 to 50 parts by weight based on 100 parts by weight of the inorganic particles.

6) Coating method

Coating method of the coating composition according to the present invention comprises the steps of forming a binder solution; Forming a coating slurry; It consists of forming a porous coating layer.

In the forming of the porous coating layer, the slurry formed in the coating slurry forming step is applied to at least one surface of the porous substrate to form a porous coating layer.

Porous substrates can be used as previously described herein for separators.

The method of coating the slurry on which the inorganic particles are dispersed on the porous substrate may use a conventional coating method known in the art, for example, dip coating, die coating, roll coating, comma Various methods can be used, such as a (comma) coating or a mixing method thereof. In addition, the porous coating layer may be selectively formed only on both sides or one side of the porous substrate.

The coating process is preferably carried out at a certain range of humidity. After coating of the slurry, binder A and binder B according to the present invention dissolved in the coating layer (slurry) during the drying process are different phase transitions by vapor-induced phase separation phenomenon known in the art. Will have characteristics. In general, the non-solvent (e.g., moisture or vapor) phase transition rate is higher with higher HFP content, resulting in lower phase separation rates under the same nonsolvent, and the amount of nonsolvent required for phase separation is also relatively high. You will need a lot. As a result, binder A having a low HFP content is phase-transformed by a relatively small amount of non-solvent and has a high speed, thereby distributing more structures than binder B on the surface of the resulting porous coating layer, thereby forming a structure of an adhesive layer, and relatively HFP content. This high binder B is required to have a large amount of non-solvent required for phase separation and is relatively slow, and thus is present in the inside of the porous coating layer more than binder A. Therefore, according to one embodiment of the present invention, a structurally stable porous coating layer and a binder layer having excellent adhesion to the electrode is formed on the porous coating layer. When the weight ratio of HFP in binder A is 80% or less of binder B, it may have a distribution tendency of a desired binder as described above.

However, in the case of less than 3㎛ and the thin film and low-humidity can not achieve the desired purpose simply by the difference in the content of HFP. In the binder according to the present invention, the binder A having a low HFP content is even lower than the number average molecular weight of the binder B, so that the phase transition may occur rapidly even at a short drying time of the thin film coating having a thickness of 3 μm or less, and the speed may be faster. When the number average molecular weight of the binder A is 70% or less of the binder B, the desired physical properties can be obtained even when the thickness is 3 μm or less and the thin film and the low humidity.

Drying can use methods known in the art and can be carried out batchwise or continuously using an oven or heated chamber in a temperature range that takes into account the vapor pressure of the solvent used. The drying is to almost eliminate the solvent present in the slurry, which is preferably as fast as possible in view of productivity and the like, for example, may be carried out for a time of 1 minute or less, preferably 30 seconds or less.

As such, the separator of the present invention prepared by the above-described manufacturing method can be used as the separator of the electrochemical device.

That is, the separator according to an embodiment of the present invention may be usefully used as the separator interposed between the positive electrode and the negative electrode.

7) Electrochemical Device

Electrochemical devices include all devices that undergo an electrochemical reaction, and specific examples include capacitors such as all kinds of primary cells, secondary batteries, fuel cells, solar cells, or supercapacitor devices. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the secondary batteries is preferable.

The electrochemical device may be manufactured according to a conventional method known in the art, for example, it may be manufactured by injecting an electrolyte after assembling through the above-described separator between the positive electrode and the negative electrode.

The electrode to be applied together with the separator according to an embodiment of the present invention is not particularly limited, and according to a conventional method known in the art, the electrode active material may be prepared in a form bound to the electrode current collector. Non-limiting examples of the positive electrode active material of the electrode active material may be used a conventional positive electrode active material that can be used for the positive electrode of the conventional electrochemical device, in particular lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or a combination thereof It is preferable to use one lithium composite oxide. Non-limiting examples of the negative electrode active material may be a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, in particular lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorbents such as graphite or other carbons are preferred. Non-limiting examples of the positive electrode current collector is a foil produced by aluminum, nickel or a combination thereof, and non-limiting examples of the negative electrode current collector is produced by copper, gold, nickel or copper alloy or a combination thereof Foil and the like.

The electrolyte solution which can be used in one embodiment of the present invention is a salt having a structure such as A + B-, A ⁺ includes an ion consisting of an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ or a combination thereof, B ^- is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, AsF 6, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C Salts containing ions consisting of anions such as (CF ₂ SO ₂ ) ₃ ^- or a combination thereof are propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl Carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (?) -Butyrolactone) or a mixture thereof, or dissolved in an organic solvent, but is not limited thereto.

The injection of the electrolyte may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and the required physical properties of the final product.

<Example>

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited to these Examples and Experimental Examples. Embodiments according to the present invention may be modified in many different forms, and the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to fully explain the present invention to those skilled in the art.

1) Preparation of Binder

Example binders according to the present invention and the binder solutions of Comparative Examples 1 and 2 were prepared as follows.

Example Binder

Binder A: PVDF-HFP, molecular weight 400,000, HFP content 8%

Binder B: PVDF-HFP, molecular weight 900,000, HFP content 14%

The mixed weight ratio of binder A and binder B is 1: 1

<Comparative Example 1 Binder>

Use only binder A of the example

<Comparative Example 2 Binder>

Use only binder B of the example

2) Preparation of Coating Layer

<Compare results>

Binder A and B were mixed in a 1: 1 weight ratio, added to acetone, and dissolved at 50 for about 4 hours to prepare a binder solution. As an inorganic material, 500 nm Al ₂ O ₃ powder and 250 nm Al ₂ O ₃ powder were mixed in a 9: 1 weight ratio and added to the binder solution such that a weight ratio of polymer binder: total inorganic particles = 1: 4. A slurry was prepared by adding cyanoethylpolyvinyl alcohol to 10 wt% of the total amount of PVDF-HFP binder and then crushing and dispersing the inorganic particles using a ball mill method for a total of 12 hours. At this time, the ratio of solvent and solid content was set to 4: 1.

The slurry of Comparative Example 1 and Comparative Example 2 was prepared using the same method except for the binder.

Each slurry to which the binders of Example, Comparative Example 1 and Comparative Example 2 were applied was used to coat 3, 4 and 5 탆 based on the cross section at 45% humidity and 3 탆 based on the cross section at 35% humidity. It was. The surface of the coatings of Examples, Comparative Examples 1 and 2 related to this were measured by electron microscope and shown in FIGS. 2, 3 and 4, respectively. 2 shows good coating even at 3 μm and humidity of 35%, and Comparative Example 2 did not show satisfactory coating results under all conditions.

Preparation of electrodes using the coating compositions of Examples, Comparative Examples 1 and 2, followed by ER (resistance, ohms), electrode-membrane adhesion (gf / 15 mm), and peel strength (gf / 15) for each electrode Mm) was measured. In Example 1 only low-humidity, 3 ㎛ thin film coatings showed similar physical properties, Comparative Examples 1 and 2 showed a problem showing a sharp drop in adhesion. Comparative Example 2 exhibited a problem that not only the adhesion was too low overall, but also decreased further in the thin film coating.

As described above, only by the invention according to the present invention, it was confirmed that the low-humidity, even the thin film coating shows excellent physical properties.

The present invention increases the bonding force between the porous coating layer and the electrode of the separator to increase the safety due to the strong integration of the separator and the electrode and to suppress the increase in the interfacial resistance of the separator and the electrode by the electrode side reaction generated during the cycle, improving the air permeability binder It can provide a coating composition comprising a. In particular, when the film is thinned from 4 μm to 3 μm, the binder is dried before sufficient phase separation and sufficient electrode adhesion cannot be obtained. Also, in the manufacturing method, a coating composition capable of sufficient phase separation even under low humidity conditions is provided. .

Claims (13)

In the coating composition comprising a solvent, inorganic particles, a dispersant, a binder for coating at least one side of the porous substrate having a plurality of pores, The binder includes binder B and binder A, Binder B and binder A both include vinylidene fluoride (VDF) derived units and hexafluoropropylene (HFP) derived units, The HFP-derived unit occupies 8 to 50% by weight of the binder B, in the binder A is 80% or less of the ratio of the binder B and at least 5% by weight of the binder A, The total number average molecular weight of binder B is 200,000 to 2 million, the total number average molecular weight of binder A is 70% or less of binder B, The coating composition in which the weight ratio of binder A: binder B in the total coating composition is 0.1 to 10: 1. The method of claim 1, The binder B and the binder A is a coating composition consisting of vinylidene fluoride (VDF) and hexafluoropropylene (HFP). The method of claim 1, In addition to binders B and A, vinylidene fluoride-derived copolymers including PVDF-CTFE, PVDF-TFE, etc., polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone , Polyvinyacetate, ethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate (cellulose acetate propionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose (carboxyl methyl cellulose), acrylonitrile-styrene-butadiene copolymer A coating composition comprising (acrylonitrile-styrene-butadiene copolymer) and a polyimide, each alone or a mixture of two or more thereof as an additional binder. The method of claim 1, The porous substrate is polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polyamide, poly Carbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polybenzimidazole, polybenzimidazole Any one polymer selected from the group consisting of polyethersulfone, polyphenyleneoxide, cyclic olefin high polymer, cyclicolefin copolymer, polyphenylenesulfide and polyethylenenaphthalene Tombs formed from mixtures of more than one species Film or a multi-film, a woven or non-woven fabric in a coating composition. The method of claim 1, Coating composition wherein the dispersant is one or a mixture of two or more selected from the group consisting of acrylic copolymers. The method of claim 1, The inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transfer ability, and mixtures thereof. The method of claim 1, A coating composition consisting of two or more kinds of inorganic particles having different sizes. The method of claim 1, The coating composition has a content of 3 to 50 parts by weight based on 100 parts by weight of the inorganic particles. The method of claim 1, The coating composition has a content of 0.5 to 5 parts by weight based on 100 parts by weight of the inorganic particles. Separation membrane coated with the coating composition of any one of claims 1 to 9. The method of claim 10, Separation membrane having a thickness of 3㎛ less than the cross section. An electrochemical device comprising an anode, a cathode, and the separator of claim 10 interposed between the anode and the cathode. The method of claim 12, The electrochemical device is a lithium secondary battery.

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